The characteristics of a data input/output buffer in a semiconductor memory device vary in accordance with changes in a process voltage temperature (PVT). When the characteristics are out of proper range, high-speed data transfer becomes difficult. For this reason, there is a need to bring the characteristics of the input/output circuit back into the appropriate range by correcting for the changes in the characteristics of the input/output circuit.
According to one method, a zero quotient (ZQ) calibration function has been proposed. The ZQ calibration is a method that dynamically corrects the impedance of the signal line of the input/output circuit using a termination resistor connected to the signal line of the input/output circuit.
However, during the ZQ calibration, the input/output circuit cannot be used. For this reason, when the ZQ calibration is frequently executed, the data transfer by the input/output circuit cannot be executed, and thus the data transfer is limited.